1. Field of the Invention
The present invention relates to in vivo tissue fastening in which one tissue is brought closer in respect to, and fastened to, a second tissue.
The present invention particularly relates to the fastening of a soft tissue to a hard tissue, such as tendon to bone, wherein, by separate action transpiring at the two ends of a fastener device, (i) a one end of a fastener is firmly permanently compressively anchored in the hard tissue (bone) while (ii) a large area of the soft tissue (tendon) is drawn toward the hard tissue--including by an efficient sliding motion--at a selected tension (compression) force--including as may be obtained by action of screw threads--so as to, typically, compress the soft tissue (tendon) to the hard tissue (bone) at an adjustably variable compression force.
The present invention still further particularly relates fasteners for the fastening of a soft tissue to a hard tissue, such as tendon to bone, that are both (i) physically substantial and robust in all sections, and (ii) exhibit bending and torsional movements, that are in all respects eminently suitable for implementation in certain plastic and/or in collagen (artificial bone) materials that, nonetheless to being well tolerated by and absorbable within the body, are neither so physically strong nor so flexible as are, for example, metals.
2. Description of the Relevant Art
2.1 Orthopedic Connection to Bone
Since the middle of this century, orthopedic research has advanced and proven the importance of "primary" bone union versus &non-primary" bone union. The former connotes a healing in which the bone portions are held in close alliance and with rigidity and stability in relationship to each other. With these conditions met, the fractured bone will immediately bridge the gap between the bone pieces so that all the new bony material is dedicated to bridging and virtually none is wasted to create a temporary "splint" of material around the fractured bone.
Non-primary bone healing occurs when the bone portions are not held rigidly with respect to each other. In this case, the bone cells will initially lay down a doughnut-shaped "splint" of bone-like material around the fractured pieces in order to create a rigid relationship between the bone portions. Once the portions have been immobilized, the bone cells will then become bridges. Finally, after this process is completed, the bone will gradually resorb the doughnut-shaped splint.
Many companies manufacturing orthopedic appliances have created metal bone plates and screws which, when deployed, create a stabile, immobile environment for the bone portions, promoting the very desirable primary bone fixation. While it has been shown that when the bone portions at the fracture interface are brought within a close proximity, there is optimal healing speed and achievement of optimal strength within a short period of time, because of the nature of prior art screws--which rely on non-measurable and often nonadjustable shear forces to accomplish fixation--there has been little investigation into the optimal pressure and gap in order to achieve the optimal healing speed and strength.
A more recent orthopedic concept advanced has been to create a low grade electrical current between fractured bones which are undergoing the bridging process. The electrical current apparently does not influence whether a primary or a non-primary union is created. However, the current prompts the bone cells to begin the healing process, and speeds the healing process once underway. A number of companies have developed electromagnetic coils which are often placed around the skin nearest the bone fracture which will help to guide the bones into a healthy healing.
Other factors which affect bone healing are the nutrients available to the bone cells, the acid environment around the fractures, the potency of the blood supply, the bone density and the area of the bone fracture, whether at the spongy end bone, in the mid-shaft hard, tubular bone or in flat bones characterized by the bones of the skull. Many of these factors cannot be influenced by the orthopedic surgeon and generally, orthopedic fixation technique has been directed towards (i) rigid plating in many types of fractures and (ii) the use of elector-magnetic current in either cases of soft bone (such as in geriatrics where there is an anticipated slow healing process) or in multiple fracture fragments where there may be bone fragments missing or crushed.
As noted, the screws used in this fixation, either of bone to bone, tendon to bone, ligament to bone or joint capsule to bone, are generally not adjustable in the compressive pressure that they apply to meld the bone structures together. Yet is clear that there is an optimal gap configuration between bone portions and there is also an optimal pressure between the bone portions which will promote the optimal healing situation.
The orthopedic fastener devices of the present invention will be seen to have combinations of bone anchors and "adjustable cinch buttons" (as will be explained). These fastener devices will be seen to provide easy-to-adjust compressive forces between two in vivo structures, including adjustment at a time following implantation. A variety of fastener devices will be seen to be presented, all designed to provide various mechanisms for fixating in vivo structures through modified bone anchors joined to a moveable button. Once the existence of fastener devices in accordance with the present invention--which can easily provide adjustable and easily replicated pressure on healing portions--becomes known, it is the contention of this author that the benefits of the theory of the fastener device will become appreciated, and that further investigation into the optimal compression for the healing pressure will be made so that surgeons can effectively heal even the most difficult cases.
This concept of adjustable compression on healing in vivo structures is believed to be most important in geriatric orthopedic surgery where the patient has soft bones which do not heal quickly, but at the same time, cannot be immobilized for long periods to promote proper fixation without risking embolism or vascular accident. Once the correct compressive force is determined, surgeons will have one more important concept with which to influence the speed of healing.
The present invention will be seen to further relate to in vivo tissue fastening in which one tissue is brought closer in respect to a second tissue. In fastening a soft tissue to a hard tissue, such as tendon to bone, the fastener device of the present invention will be seen to be configured in a novel manner at both its ends. One embodiment of the invention will be seen to consist of a shaft which has at one end (i) a novel expandable collet which expands so as to provide anchoring to the bone, and which has as a second end (ii) a "sliding button cinch anchor" that brings a soft tissue toward the bone and then clamps against the shaft, holding the tissue in position through compression of a large surface area of tissue. Examination of particular prior art of relevance to these features, as transpires in the next following sections, is thus of relevance.
Yet another novel feature of the present invention will be seen to be that the shaft and the "button cinch" can be threaded so that, following the sliding of the button cinch onto and along the shaft, it can be secured in such a manner as to be able to be screwed on the shaft in the manner of a nut, providing incremental compression of the secured tendon. In one embodiment of the fastener device of the present invention, it will be seen that a hole can be drilled entirely through the bone, one end of threaded shaft which ends in an eyelet or hook is passed through the bore in the bone and attached to a tendon while a threaded button cinch at the opposite end of the shaft sits on the bone surface around the bore. The amount of tension applied to the tendon may be adjusted through rotation of the threaded button on the shaft. The particular prior art to this feature will also thus be of relevance.
2.2 Reference and Relation to the Inventor's Own Related Patent Applications
The easy-to-use two-ended fastener device of the present invention is an evolution of two prior patent applications of the same inventor Yosef Freedland.
The first application was filed Mar. 23, 1992, as Ser. No. 08/034,269 and the second was filed on Jan. 21, 1994 as Ser. No. 08/184,121. The first of the two applications deals with bone anchoring devices which are distinguished in that "wings extend beyond the [deployment] sleeve". While the present invention also incorporates this deployment method and is a Continuation-in-Part of the 1993 patent filing, the anchoring end has been modified so that it can work in conjunction with a sliding button cinch arrangement.
The latter of the two related applications, Ser. No. 08/184,121, deals with a sliding button cinch device at the opposite end of a shaft to which an anchoring device has been secured such that the button can provide an adjustable compressive force on a bone or tendon surface. The button cinch was configured in a manner in which tabs on the button would, through a ratchet action, slide up a ratchet shaft to be held in position. The button cinch was unique both in configuration and in providing a new concept in tissue fixation, namely the provision of adjustable and measurable tension or compression on tissues following implantation of a fastening device. This concept is carried forward in the present invention.
Such a characteristic of adjustable tension or compression in the joining of tissues is exceptionally important in that medical science is now recognizing that the healing of fractured or torn tissue proceeds under specific amounts of many factors including change in electrical potential of the bone, distribution of chemotactic materials and specific amounts of tension or compression which cause the tissue to heal and reorganize the reparative cells with specific architecture to support and join the fractured or broken parts such that the specific forces which come together at the site of the injury are neutralized.
By providing specific tension or compression levels at the site where repair must take place, it is presumed that the healing will take place fester and that the architecture of the repair will be manufactured by the body in an optimal fashion which will more closely resemble the final configuration of those tissues following complete healing and removal or dissolution of the fastener device hardware.
2.3 Description of Prior Art
Various orthopedic fasteners are known which bring tissues closer together. Spreading anchors are common, and are characterized by the Mitek anchor which has fins which are compressed into a bore in the bone. While it is pushed to its placement, the bore of the bone maintains the fins in the compressed state. When the anchor has achieved its position, the suture which is attached to the anchor is pulled upon so that the fins spread outward into the adjacent bone and provide an anchoring. This suture is then threaded into the soft tissue so that the soft tissue is approximated to the bone. The suture is then tied to maintain the soft tissue against the bone.
This common type of bone anchor has several drawbacks. First, the fins of the device drag in the bone, likely leaving debris which will cause body cells to congregate to remove the debris leading to bone thinning around the implant, leading to implant movement over the long term. Second, the suture is passed through the soft tissue and knotted, and can create point pressure on the tissue and cut loose through the strands of the tendon. Third, the ultimate strength of the anchor is limited to the strength of the suture material which has a low pullout failure strength. Fourth and finally, upon dissolution of the suture the implant becomes an unattached moveable piece that can migrate through bone.
Another class of orthopedic fasteners are made of plastic and thus have the advantage of being radiolucent so that the postoperative radiograph shows a clear, unobstructed suture site. This should be contrasted with metal anchors that block the complete field direction behind the anchor. Again, this class of anchor uses suture to attach the tissue to it. These plastic anchors rely on partial shear and compression forces to achieve fixation in soft bone, and are thus less resistant to being moved or dislodged than would a fastener that was forced, especially compressively forced, against hard bone.
Still another class of orthopedic fasteners relates to those which can dissolve following a specific period of time in the tissue. There are a variety of materials which can be used to achieve this dissolvability of which, at the present time, polyglycolic acid (PGA) which is a common suture material, is the material often utilized. Anchors which dissolve over time are characterized by the experimental Lactosorb under investigation by U.S. Surgical, and by the dissolvable TAG sold by Acufex. As noted, these devices, are put into the bone under compression and are abraded by the surrounding bone as they are put into place and expanded. This process develops microscopic debris. This debris has a tendency both to cause (i) premature immune cell response, and (ii) micro-fissures in the implant causing joint damage and susceptibility to early break-up. In the case of the Acufex TAG, the device is formed as a simple ridged barrel with a suture attached. The barrel is pushed into the bore in the bone and the rigid rings prevent back out of the implant. The anchoring portion of the adjustable button cinch anchor fastener in accordance with the present invention will be seen to be similar to the Mitek anchor in that it achieves its anchoring through expansion of fins or flukes into bone adjacent to the bore drilled in the bone. However, it significantly differs in that the flukes are in a collapsed state during the insertion and are not held in this state by the pressure of the walls of the bore. When and only when the adjustable button cinch anchor fastener achieves its proper position, the shaft is pulled upon to cause the flukes to spread radially outward into the adjacent bone through a cam action of the shaft on the flukes. This is a superior method of deployment as the scraping and scratching of the anchor surface is avoided, preventing the immediate release of microscopic debris in the adjacent tissue, leading to early tissue reaction to the implant. Moreover, and furthermore, the direction of the spreading will be see to be so as to present a greater diameter of the anchor in the direction of the opening of the bore in which the anchor is lodged, and towards the hard bone at the surface opening of the bore. This makes that the anchor maintains its position in bone not only in compression, but also in compression against lard, as opposed to soft, bone.
The securing end of the adjustable button cinch anchor fastener of the present invention will also be seen to differ from the Mitek anchor in that it does not rely on the threading of the soft tissue onto the suture and knotting to hold it down. Rather, it has a compression button such that the soft tissue is held against the bone with a compressive force spread over the surface area of the compression button. This offers significant advantage over suture knots in that the point pressure of thin threads is absent, allowing a more stable fastening of the soft tissue.
Yet another subgroup within this group of fasteners are the winged bolts in which the device is wholly removable following use. Some of the devices which characterize this quality are the subject of U.S. Pat. No. 4,409,974 for a BONE-FIXATING SURGICAL IMPLANT DEVICE to the selfsame inventor of the present application under his former name of Jeffrey A. Freedland, and also under U.S. Pat. No. 5,098,433 under the same inventor's present name, Yosef Freedland.
The fastener of the present invention will be seen to differ from these previous devices for, inter alia, having fewer moving parts here. The design of the fastener of the present invention will be seen to lend itself to manufacture from plastic and dissolvable materials. In the first place it has and presents a greater bulk that is useful for fabrication with these materials. In the second place, it does not require a great deflection or other forcible distortion of moveable portions or pieces to achieve an anchoring effect, thus permitting the use of plastics that are slightly brittle. Several layers of operating mechanisms would be very large compared to metal devices. Further, the opposite end of the anchor, to which the second tissue was attached, either consisted of a knotting of suture, or a threaded nut arrangement. In the case of the Orthopedic Fastener, the compression button can be pushed into placed and secured without turning it on a threaded shaft.
Further, in its preferred embodiment, the Adjustable Cinch allows tension to be adjusted following implantation which is unique in the anchor market. This is particularly useful in multiple fractures where several pieces of bone must be aligned in order to get an appropriate result. As the pieces are put into place, previously placed fixation devices can be re-adjusted in tension level to permit the pieces to fit better.
The adnustable button cinch anchor fastener of the present invention will be seen to have the shaft that can easily be manufactured from a material such as plastic which can be cut to any length following implantation. This allows it to be a one-size-fits-all implant while maintaining the unique ability to be adjustable in its compressive or tension force following implantation. Indeed increasing tension or compression can be made even following cutting the excess shaft.
In yet another embodiment of the adjustable button cinch anchor fastener of the present invention, the bone anchor will be seen not to use a wing. In this case, the shaft has only a compression button at one end and a direct receptacle for soft tissue in the shaft on which the compression button sits. This type of shaft offering an adjustable compression method is noted in my patent which was filed Jan. 21, 1994 under Ser. No. 08/184,121. This previous application teaches to the general concept of a fastener device which applies adjustable tension or compression on a tissue following implantation of the device. However, the device taught within the predecessor application relies on a simple threaded nut arrangement to provide this adjustable force. This arrangement is sub-optimal because it takes a long time for the surgeon to install, perhaps as much as four minutes longer than an adjustable button cinch anchor fastener in accordance with the present invention.